1. Field of the Invention
The present invention relates to a method of analyzing frictional energy in a contact surface of rolling tire which is dissipated as wear of tread rubber.
2. Description of the Related Art
There are following technologies of predicting wear of a surface of a tread of a tire.
According to a first method, a tire is rolled in a state in which a coating is regularly coated on a surface of a tread of a tire, a degree of abrasion of the coating is recorded as a plurality of pieces of image information at required time intervals, the respective pieces of image information are divided into a number of pixels and stored, the respective pixels in correspondence with portions coated with the coating, are weighted with a magnitude inversely proportional to a time period of abrasion of the coating, further, such an abrasion information at the portions coated with the coating is converted into abrasion information in a wide region expanded to respective pixels including also portions not coated with the coating by calculating an abrasion level value in consideration of weights of their own and weights of peripheral pixels with regard to the respective pixels including the portions not coated with the coating, and the respective abrasion level values are constituted into a map to thereby predict a situation of causing irregular wear at the surface of the tread by the mapped information (U.S. Pat. No. 5874670).
According to a second method, a coating having a brightness which differs considerably from that of a surface of a land portion and deformed by following deformation of the surface of the land portion, is regularly coated on the surface of the land portion of a tire in a shape of lattice, net mesh or dots, thereafter, the tire is additionally rolled on a road surface and a situation of causing wear is predicted from a degree of abrasion of the coating (Japanese Patent Laid-Open No. 08029296 A/1996).
In both of the first and the second methods, a coating is coated on the surface of the tire and the state of wearing tire is predicted thereby and therefore, there poses a problem in which the coating must be coated in the measuring operation.
A third method is a method in which wear of a tread band of a tire is predicted and controlled based on a cut-in portion having a shallow depth formed on an outer face of a tread band at a thickness portion of a material like elastomer (U.S. Pat. No. 5801304).
According to the third method, a plurality of cut-in portions in the radius direction need to be formed at portions on an outer face of the tread band in the radius direction and there poses a problem in which the method is not preferable as the method of analyzing the surface of the tire.
According to a fourth method, a sum of frictional energy is calculated over an entire contact length to substitute for wear energy.
The method is as follows specifically.
A wear shape of a tread is predicted by measuring pressure and displacement in the forward and rearward direction and the left and right direction within the contact patch accompanied by rolling the tire by sampling at constant intervals and depending on a sum .SIGMA.E of frictional energy at respective measuring points by a calculation using the data and an in-plane distribution thereof.
A generally known calculating method is as follows.
Frictional energy .SIGMA.E is calculated as a sum of integrating frictional energy at respective sampling intervals provided with an inner product of displacement vectors calculated from difference values of measured displacements and in-plane pressure vectors from a front end to a rear end of contact. When the integrated value .SIGMA.E is regarded to correspond to frictional energy dissipated in the contact patch, a wear amount of tread rubber seems to be proportional thereto.
That is, the frictional energy .SIGMA.E is represented by the following equation. EQU .SIGMA.E=.intg.Pxy.multidot.dS
Incidentally, integration is carried out by a sum within the contact length L.
However, according to the fourth method, there poses the following problem.
In the case of a heavy load tire (hereinafter, referred to as TB tire) satisfying a wide condition of use from a short distance (short life) to a long distance (long life) and supporting a heavy load by the same tire, there causes inconsiderable occurrence of running slippage as in a small-sized tire for low load, which does not necessarily coincide with a result of analysis.
What seems to be the cause of the in coincidence resides in that the frictional energy is integrated throughout the contact patch.
That is, the frictional energy is integrated over the entire contact length on the premise that slippage is caused over the entire contact patch. In comparing a property of a small-sized tire having low rigidity/low load which is liable to cause slippage inherently with a result of wear test integrated with intentionally slipping curved running, such an analysis method is less problematic. Further, rubber compound of a small-sized tire is softer than that of the large-sized tire and the small-sized tire is worn when excessive vertical pressure is applied. Accordingly, the fact of requesting uniform dispersion of the ground pressure seems to be the reason compatible with the analysis of the small-sized tire.
Meanwhile, a large-sized tire having high rigidity/heavy load is provided with a totally inverse property in which in-plane slippage is extremely small even under an excessive vertical pressure and energy loss dissipated by the frictional energy is small. Small rolling resistance per load of a TB tire also supports the fact.
Further, even in the case of a TB tire, a block pattern of a rib-lug-type, above all, all weather type constituting a main current domestically shows a property similar to that of a small-sized tire in the use of a tractor head requiring a small turning radius and high traction performance.
In order to cover such a wide condition of use and property, there is needed a method of setting a region of a calculation object for differentiating an adhering region having small slippage from a slipping region causing slippage and taking out only wear energy contributing to wear of tread.
Hence, in view of the above-described problem, the invention provides a method capable of easily analyzing frictional energy of a rolling tire.